1. Field of the Invention
The present invention relates to conversion of the scan line format of a digital video signal, for example as between a format of sequential frames, each frame being a pair of interlaced video fields, and a format of non-interlaced (or "progressive") video frames. The invention is of particular utility for conversion as between the presently contemplated HDTV format of 1050 scan lines per frame of paired interlaced fields at a field frequency of 60 Hz, and a progressive frame format of 525 scan lines per frame at a frame frequency of 30 Hz.
2. Description of the Related Art
There are various situations in which it is necessary to change the scan line format of a video signal. It may be sought to increase the apparent definition of the image, which necessitates increasing the number of scan lines. Conversely, it may be necessary to reduce the number of scan lines in order to limit the signal bandwidth to that of the transmission channel over which the video signal is to be transmitted to a receiver. A more recent situation requiring scan line conversion relates to HDTV signal transmission, since the HDTV format does not match that of a standard NTSC signal and so must be converted in order to be capable of reception by existing television receivers. This, in turn, means that an HDTV receiver must include a decoder for re-converting the received video signal back to the HDTV format.
It is expected that the HDTV system will be digital; i.e., the transmitted video signal will be in the form of data code words which signify luminance and chrominance of each of the pixels in the video image. Scan line format conversion will therefore require anti-aliasing filtering, subsampling and interpolation, which operations inevitably introduce temporal artifacts in the video image. It would therefore be advantageous to limit such operations to only so much of the video signal data as is absolutely necessary in order to achieve the necessary format conversion, and to minimize processing of the remaining data. This will also have the advantage of permitting considerable simplification of the format conversion apparatus.